1. Field of the Invention
The present invention relates to a semiconductor device used for, for example, a frequency of 300 MHz to 1 GHz, which can be easily manufactured and has a high-frequency characteristics.
2. Description of the Related Art
A semiconductor device on which an integrated circuit such as IC or LSI is formed is contained in a package of ceramics or the like. FIG. 1 is a plan view showing a conventional semiconductor device, and FIG. 2 is a cross sectional view taken along the line II to II.
A semiconductor substrate 1 of, for example, a silicon semiconductor, is bonded to a cavity portion 9 at a central portion of a substrate mounting portion 2 consisting of a ceramic substrate of, for example, aluminum nitride, via a conductive adhesive 7.
For example, a lead 3 made from a lead frame of an Fe alloy containing Ni by 42 wt %, is bonded to a periphery portion of the substrate mounting portion 2 by an insulation sealing member 4 made of, for example, glass. A plurality of leads 3 are arranged around the semiconductor substrate 1 with intervals between adjacent leads.
At end portion (inner lead) of each of the leads 3 is connected to a connection electrode 40 on a surface of the semiconductor substrate 1 via a bonding wire 5 of Au, Al or the like. The leads 3 are used as various types of power source wires and signal lines.
Among the grounded ones of the leads 3, leads a arranged at corner portions of the semiconductor substrate 1 towards the central portion thereof, usually serve as supports for a lead frame, and are not used as leads, but in a floating state even after completion of the semiconductor device. For this reason, generally, no lead wires are provided for the corner portions.
The substrate mounting portion 2 is bonded to a cap 6 with the same material as the sealing member 4 used for bonding the lead 3. The cap 6 has a recess portion, and the main surface thereof, which is bonded to the substrate mounting portion 2. In the recess portion, the semiconductor substrate 1, the inner lead portions of the leads 3 and the bonding wires 5 are contained, and they are sealed therein. The cap member is made of ceramics made of the same material as that of the substrate mounting portion, such as aluminum nitride. Further, the semiconductor substrate 1 mounted in the cavity portion 9 at the central portion of the substrate mounting portion 2 is bonded to the substrate mounting portion 2 with the conductive adhesive 7.
Recently, semiconductor devices are, in many cases, used at high frequency. Under such circumstances, in the conventional semiconductor device, leads made from a lead frame are used as power source wires, thus causing a large inductance and increasing noise. Furthermore, only the leads are used as transmitting paths for the integrated circuits formed on the semiconductor substrate. Therefore, when such a semiconductor substrate is used for a frequency band of 300 MHz or higher, it is required to ground (GND) at least one of every four leads so as to prevent the resonance. Therefore, in this case, 1.25 times more leads than it is usually needed are required. Furthermore, for a frequency of 500 MHz or higher, the matching of characteristic impedance must be taken in consideration of transmission characteristics. Therefore, at least one of every two lead must be grounded, thus requiring twice as many leads as it is usually needed.
Moreover, several signal lines are provided between power lines, especially, leads which serve as GNDs; however the distance between a GND and a signal line varies from one case to another, and the arrangement of these lines is asymmetrical. Therefore, when the frequency exceeds 300 MHz, the lines are resonated with each other, making it impossible to achieve the matching of impedance.